@MrsHuntGeneNotJeremyObviously
Going against the grain but I think it was wholly inappropriate to say that to his DD when he is in another long term relationship. There are ways of comforting his child, without disrespecting his current partner. He could have said that she meant a lot to him too, that he regretted the way things ended, without using 'love of my life'.
I wouldn't want to be with a man who saw me as his second choice or who gave that impression about our relationship to other people (even his own DC).
Yes, snooping is wrong, but I would want to discuss this with him before committing even more of my life.
Call me cold, but I'd not be expecting to give emotional support to my partner because his ex wife died. I'd expect him to be a bit sad because of shared history, but full on grief? No, I'd expect him to not be feeling that level of emotion if he'd been divorced 9 years and in a relationship with me for 7!
I would expect my support to him to be focused on how best to help the children.
I actually agree with this.
That phrase "love of my life" has the potential to cause a lot of problems, even if OP had never seen it.
For all of you trying to explain it away as "Well, she was the love of his life then" and all the other ways of twisting it, you're forgetting that his DD will not be taking the phrase as anything other than face value. Why would she, she trusts her dad.
And the DD may, in her grief, start seeing the OP as an interloper, who had prevented her parents getting back together, which would sour any relationship between OP and the DD. OK, that's one possibility, there are others.
There are many ways he could have comforted his DD, but that particular phrase isn't one.
If I were in OP's shoes, the worry I'd have right now is that the DP will, in his grief, put his ex on a pedestal. That would have a lot of impact on his relationship with OP. I wouldn't stay in a relationship where I became second best.
OP, I suggest you support him to support his DC, and maybe watch how your relationship progresses through his grieving. If he does start to put his ex up on a pedestal, thats something real in your relationship you can talk to him about, without mentioning the message you saw on the phone.