Not being able to keep friends?

Yesterday I had someone try to read my personality and the most shocking realization he gave me was this line: "You have no friends."
My immediate response was "No, I have a lot of-" to which he cut me off by saying, "You have no real friends."
Which, I stopped to think, is striking the nail on the head.

First off, I have no problem with making friends. The problem seem to be in keeping them. I have this cycle where, when I go to a new place or environment (let's say new class, tennis club, social circle, etc) I suddenly become one of THE most likeable people and EVERYONE is, or wants to be, my friend. Then for several months I stay as part of that crowd, and people just won't stop asking me out, etc. But after let's say 4-5 months of too much hanging out, I get bored and irritable and prefer to 'retreat' to my introvert self and people begin to ask stuff like "What's wrong?" thinking there's some problem going on in my life, thinking I'm just down or moody, and in my mind I reply with "Nothing, I just can't be bothered anymore." They'd keep pestering me, trying to 'cheer me up' out of my retreat, then after a while they stop. For some it takes longer, like several months, before they'd stop trying.

You'd think that I'd start to miss social interaction with them, but frankly, I don't, and I don't really want to hang out with anyone that I got 'bored' of anymore. I don't even feel slightly guilty about it, and if anything the fact that I'm not guilty is what I'm feeling guilty about. I'm almost 21 years old now and I've moved schools and universities around 9 times, and I have not retained any proper friend from any of them. However, I'm on good terms with most of them (most that doesn't mind being ignored for a long time, and by long I say years) so sometimes out of the blue I may ask them to hang out with me, they'd ask "Where have you been?!" then we'd hang out as if we never stopped hanging out in the first place.

I never minded this trait about me, but very recently, I 'lost' my best friend of 8 years when we went on our first staycation together. We've been friends since middle school and it was our first time together somewhere. He goes to university in Holland and I went to Singapore, so for around 3 years we've been keeping contact on Skype EVERY. SINGLE. DAY. And I mean, every day we would skype for 8 hours regardless of our timezones. So I always believed this was the one friend I wouldn't give up the world for, and I'm viciously protective of his friendship with me and am very jealous of his other friends too.
Anyway, on the staycation, I found that there were more things that I dislike about him than those I like. Having been in Holland for 2 years, he changed, and not really the way I liked. I mean, I changed, too, but I retained my feelings of friendship towards him, the way I interact with him, etc, but he seems to be in this phase of 'playing it cool/mysterious' which I really hate.

By the end of the vacation, he did something big which I caused an uproar about, I almost never get mad at him about anything but I really felt he went over the line. Then we didn't talk for two-three weeks or so, before he started talking to me first again, but now it's more of a 'casual friend saying hi' kind of way, not like a best friend relationship anymore.
And the worst part? I don't miss him at all!! I mean, I always thought if this kind of thing happens I would miss him, but honest to God I don't even think about our friendship anymore! And this is the best friend I always thought I'd spend the rest of my life with, going on adventures and stuff, and the only one who knows -almost- everything about me and accepts me for it.

So it scares me a bit, it being so easy to move on from friends and not feeling anything about it. Note that, during our friendship if we ever had those bickers I would miss him when we didn't talk for a few days, but it seems to be the trend that when I firmly decide to move on from someone, I just do. Then, when I get lonely again, I just call up one of my friends that I haven't talked to in a long time, or just make a new friend and go through the cycle again. Does anyone go through the same thing? Is this a BPD thing?

I have a lot of 'friends'. But at the same time, I have nobody.

Hi heavythinker....you really are a heavy thinker

I can relate to what you said. I have just a couple of close friends. I seem social but i burn out fast.

You know what, i would try to look at the positive side of it. You are able to make friends and you could even keep them - just that ''boredom'' sets in. Having social skills can be very helpful and you seem to already have that in check.

For me, the problem lays in being able to be vulnerable around people. Its hard to differentiate who you can allow yourself that with. Because with trust sometimes comes disappointment. So, we can develop friendships but not allow those to become deep enough so we dont get disappointed/hurt later on.

I am thinking maybe not throw yourself all in a new friendship and hang out with someone (or people) all the time. Maybe do it at a slower pace, where you get enough time for yourself and not end up feeling overwhelmed by all the social situations? This may give you time to cultivate a friendship a bit better while also taking your own personality into account.