Biological clock is ticking

So I'm getting to the point where it's now or never with regards to fertility and having a baby age wise. My long term boyfriend and I have a daughter together. We've gone back and forth on having another for years with him deciding that he doesn't want anymore. I have however realised that I really do want another so this is a deal-breaker for both of us. do I stay with him knowing that I will probably resent him when I can no longer have kids or do I leave and have a baby on my own via fertility treatments.