Ttc.... Any suggestions is helpful

Been trying to concieve for going 3 years now. And with no luck still haven't. I am irregular I get one every two months give or take few days. Sex every other night. We are getting tired of trying and feel to call it quits completely. It's always an arguement and it becomes stressful to talk about among each other now. So I don't bring it up to him anymore. 
 When we split up for a bit he slept with another girl one time and she got pregnant the one time they had sex. So I know he's fertile. But sad to say the girl aborted the baby to hide it from her fiancée. So he knew she did what he did and he's been different since then.