They're living together (yes already!!!) and have been for several months now. She's around every fortnight when exH has the boys and I know from what they (DS's) have said to me she does get involved, playing with them, taking them out to the park, etc etc. (I even hear rumour that she got up to DS3 when he woke in the night last weekend!!! - although I know that exH got up with him the following night)
I'm not in the slightest bit bothered by it (even when I hear "S did this with us, S did that for a week after they get back from his) , in fact it seems to be quite positive as they've been out and done stuff with exH that I know he would never have attempted to do with them on his own.
So, obviously she's involved in the boys lives, and it looks like it's going to be long term. So would it be really odd if I were to invite her to the Christening? Obviously she may not want to come, fair enough, but I do feel it would be good (for all involved) to show that I'm not at all hostile towards her, and accept that it looks like she's going to be a part of their lives long term........