I think I must live in a different world to everyone else, or maybe just have different values.
A pen, for someone who has just started retraining and so is studying is a thoughtful gift! It might not have cost a lot of money, but thought has been put into buying you something you can use, and that hopefully you'd get joy out of using.
I would stay that jewellery is generally a thoughtless gift (although there can be exceptions). It's chucking money at something, rather than thinking about something specific to someone's actual circumstances.
In our house, love is not measured by money.
We'd value something more that has been picked out that suits our specific circumstances than something that happened to cost a lot of money, but was generic.
I find the idea of an expensive present being needed to show love as quite shallow tbh.
That said, this gift obviously made you feel bad, and I think it shows that you don't feel happy in your relationship. I also picked up that in your OP you said "...and gave up my time to go with him...", when talking about your gift to him, which I also see as symptomatic of a broken relationship. DH and I really, really don't see accompanying each other to events (even if we're not particularly interested in them) as some kind of chore. We'd actively enjoy being there with each other, and I'd take great pleasure in watching my husband enjoy a show!
If my husband, in your circumstances, bought me a pen, I'd be delighted that he'd thought to get me something I could use when studying, and I'd feel lovely and fuzzy inside every time I used it. You don't feel like that, which points to far bigger issues in the relationship.
He should also have arranged to get something for you with the children. (Unless the children are 11+, in which case, they should really be doing it themselves, but even then he should probably have nudged them.)