whst should i do

so I'm 20, dating this guy who is 17, I've been around for awhile and friends with his mom. I love being around him, the sex is amazing and dare I say I love him. my ex girl friend texted me yesterday and threw me for a loop ( I've been waiting for her to come back for two years, she got married to an old friend who turned abusive and she left him ) she tells me she got a divorce a couple months back and misses me, wants the kids to be raised togeather as siblings and wants to repurpose. She makes me so happy but I'm scared of hurting my boyfriend.I have no idea If I should go back to the love of my life and get married like our original plan was when we where 17 or stay with Caleb and pursue this relationship that is based on " did mom say yes you can come over? ". WHAT DO YOU GUYS THINK I SHOULD DO ?