Fed up with my partner ex wife texting him all the time

duchy

I think you need to grow up a bit.
He obviously cares for the kids and enjoys having them around and legally arrangements for the under 18s should be made through the parent with custody anyway (not to mention it's the polite thing to do-as she may have already made other arrangements for them).
I'm guessing you don't have children or otherwise you'd understand that good parents don't stop worrying about their kids at a certain age and something like going off to uni or joining the army is a time not just that they are moving on with their lives but that parents with or without custody are going to worry a bit-and a reassuring text about money or socks is a comfort-and means the mother is keeping the husband informed-(probably knowing the son is rubbish at doing such things themselves-most teenagers it wouldn't even occur to).
Her texts seem fine to me-but his assumption that your home is open house -does sound like he's taking you for granted a bit -and maybe you're transferring that annoyance over onto his ex.
I don't have any interest in my ex's girlfriend's-why should I? Nothing to do with me except if it were to impact on my son's welfare and as you aren't even living together officially why should she take an interest ? She trusts her ex's judgement that you are a suitable person to be around their kids-so there's no further issue. Why do you expect her to be interested in you ? You say she has no "respect" for you ? Why should she-what have you done to earn it-you're a stranger to her and if they have been apart for nine years probably not the first girlfriend he's had since the split. You don't live with him-not really sure where respect comes into it apart from HIM disrespecting your home by assuming any arrangements he makes for the kids are OK with you-but that isn't anything to do with HER but to do with you and HIM !