AIBU Not To Trust DH Completely!

[Not2Trust]

As the title suggests, am I unreasonable to not fully trust my DH, as in he won’t betray my trust by having an affair?
There were a couple of instances a few years ago, which led me to feel uncomfortable with his phone interactions with a colleague and another female associate.
Reading many of the threads on here confirm why I feel the way I do, when infidelity seems to have become the new ‘norm’!
Or am I over thinking things and being unreasonable?
Maybe it’s a defence mechanism, I don’t know!

Depends on what was said? Sometimes it's with good reason to fear the worst, it can be overthinking too not every interaction with another female is anything to worry about.
I guess your gut feeling knows, if you've actually seen proof, the contact between him and another woman seems to be unusually frequent, his interest and behaviour towards you has changed?
I don't think infidelity has become the new norm, it's always been there, affairs have always happened but with forums like this we can see it's unfortunately it happens, obviously the worst of relationships make it onto these forums.

When we get trust issues it is sadly because we are not happy in the relationship, wether that is an affair or insecurity clouding judgement, what do you think it likely is?

How the heck do we know based on such scant information

If you can't trust him not to cheat on you, you shouldn't be with him. Either he's untrustworthy and you shouldn't be married to him, or you're paranoid and need help, and probably need a break from your marriage to sort that out.

Lots of women are completely taken by surprise by their husbands having an affair, but tbh if you already think there's a possibility he'd do it, if he's given you reason to think he might, then cut your losses.