Is this temporarily salvageable?

I have been with my boyfriend for five years total. The first time was 3.5 years and the second time was 1.5 years, 6 years later. The first time I left I felt that I was no longer myself and got therapy for codependency, believing that I was in a relationship with a narcissist. This second time around he has tried to convince me that he is not a narcissist, which I can go with, but now I think the real issue is his compulsive lying. On the surface it seems that the issues from today are different from those of yesteryear: sex instead of finances, but in reality it's all the same because what underlies them both are the verifiable lies. Before it was lies about looking for a job, now it is lies about the details of an affair. I think he is reluctant to tell the truth because everything about his life must be fun and telling the truth, to him, is not fun.

My fears are that I am afraid he might gaslight me in the future again, making me believe that I am crazy. I also don't like it when he tells me to go against my conscience. He has already told me to lie on his behalf (not tell my father we are dating) and keeping our relationship status off of Facebook, which led me to finding out about the "other" who capitalized on that fact.

However, that is the only real issue we have at this moment as he is fairly attentive and responsive even if it is not in the way I expect. He is very loving and affectionate, and if it weren't for his "other" encroaching on our time together with his family, I would not have thought that anything was wrong. Perhaps coming to grips with the reality is all too sudden for me as this all just became a realization to me recently.

I feel that identifying the problem is the first step toward recovery, but all I can hope for is to get through one more month so we can go on a trip we planned since the beginning of our second time together. It would give a sense of closure. Even though he suggested he might propose before we planned to get a house next year, marriage, a house, and kids are off the table indefinitely. What I am saying is that I just need to know if I can get through this month with him and get him to see that he needs help and needs to take proactive steps to combat this negative habit.