Hi k
The problem in the relationship is not only to fall in love but to keep the love and thAt takes some work . First elation of being in love does not last long ,but what is important is trust ,emotional connection,which feed your love on daily basis. He has been there for you while you shared emotional connection with someone else.give him time,he goes through the same,maybe worse,since men tend to take betrayal as offense to their masculinity and surely trust.if he loves you he will find the way to come back,but you can not do it forcefully .he has to come to terms with his own desire to share with you emotionally and physically.
Do not interrogate him,that will push him away.love him
Good luck