Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...

My best advice is to be honest with each other about your feelings and only move forward at times when both of you truly agree. Even be honest that you don't want her to take sex as meaning you two are completely okay with each other. If it happens at the right time, it might bring you closer rather than serving as a wedge.
thanks for sharing your experience :)
It may be more like guilt is making her do it.
I recommend that you spend some time with a counselor to find out what's going on.
btd - honestly, std wasn't even on my mind initially ... that boundary is in place now.
I wish you both well.