My boyfriend is a pathological liar

My boyfriend is a pathological liar, not on purpose though, he doesn’t mean to hurt anyone, and normally he ends up being hurt in the end. He lied to me about his age for over a year, just a one year difference, but he said it started in middle school cuz he wanted to be cool (I think we all do that as kids) but then he didn’t know how to tell anyone and it kept going. I’m not sure how I didn’t find out for over a year, but I didn’t. He cheated a while back and we got through it and since then he hasn’t lied and when he does he catches himself and tells the truth. It’s crazy to watch it all happen, like you can almost see his mind working and him having to stop and say no I’m lying I’m sorry. It’s usually about stupid stuff, like what he ate or who was in his class. He’s doing a lot better, it’s only been 3 months, but I can tell he’s doing better and I’m proud of him. I know it eats him up when he thinks about it, he cries about it and is constantly getting down on himself. Him and I both know he needs therapy but he can’t afford it. I know it’s not my job to be his therapist or his baby sitter, but I love him so much and I want to help him as much as I can and show him he can get better, he’s never felt like a burden, I enjoy watching him better himself. Do any of you have experience with someone who’s a pathological liar? Please no hate for staying with him, just respect my decision.

Update// I guess I wasn’t clear about the cheating situation. It was just a minor thing and it wasn’t just something I let him get away with. He did a lot to earn my trust back and still is. I don’t believe in once a cheater always a cheater because I’ve seen people come back from it. And you guys are right I shouldn’t have to tolerate it but I choose to. He’s been working really hard at getting better and I’ve already told him if he doesn’t continue to work on it and get better than I’m leaving. To me it’s similar to having any mental disorder, he can’t help it so he has to work really hard to get better. Again, please respect my decision to stay.