partner+hisex

so a couple months back id found out my partner of 4 years whoom im currently exspecting with was messaging his ex. i was fine about it until i snooped and saw the convo. she said she was getting married and his reaponce was i love you you should be marrying me ive always loved you. i wish we never broke up blah blah. anways i thought i could get over it and move on from it as he said he just felt nostalgic speaking to her again and that he didnt love her and didnt wanna marry her. what so you think could help me move on or is there no moving on should i leave ?? anyone been in this sitch have any advise.. thank you