Welcome,
I wonder why your boyfriend is worried about your ex. My AH was worried the first time he went into recovery that I would find someone else and not give him a try, that was 3 rehabs and several relapses ago.
I was agree that 2 weeks is very soon, in my opinion. I was told a great many things each time my AH went into rehab. Some were truths to lies about lies he told. ( such as he told me he lied about kissing someone else while using)
It is up to you to decide to stay, i strongly suggest to find a good support meeting and post here. When I first joined it was most helpfull.
I wish you luck, happyiness and peace.