Counter-Offer Woes

I got a new job offer that was a little less (about 5%) than my current salary. I already earn about 20% more than the median in my field/sector/age bracket.

Not exactly sure why I opted to apply, because it would be a step down "career"-wise. It would be a comfortable job where I'd know the ins- and outs of everything, but it'd probably offer few opportunities to really grow beyond that. More of an "ops" role and my current role is very much "dev"/idea guy/experiential and integrations oriented.

Asked my boss 6mo ago if I could get a $5k raise as an "ad hoc" thing. I wasn't exactly turned down, but it felt like I would have to make a huge effort to bag that - maybe that was why I went looking.

I handed in my notice with heavy heart and was really surprised by the reaction I got. Instant phone call with a 25% salary increase counter-offer and promises of a more "experimental" role, basically a free pass to be creative, try new tech etc.

These past two weeks they've tried to retain me and taken me to lunches, coffee walks- and talks, and overall been way nicer/more attentive than usual.

I know counter-offers are a mixed bag in the US, but in Europe I feel that they usually represent a true expression that the employer wants to keep someone - or at the very least that it'd be very inconvenient to lose that particular someone at this point in time. I could be wrong.

Since this is an employer I've been with for many years - my first job in fact - I was actually really emotional when I sent the resignation letter.

Now I'm worried that I'm burning bridges with the new place and scared of calling them to rescind my acceptance. They can't match the counter-offer whatsoever and it'd be an inordinate amount of overtime and late nights to get to that same level monetarily. Not sure I have that in me anymore.

I don't really have a question per se. The logical thing is to accept the counter-offer. In this case I'd both be learning and earning, for an employer that now has a more invested stake in me.

Are moral qualms like this normal?

Are employers forgiving of reneging on an already signed contract? My start date is almost 5 months from now.

Is it normal to feel bad for getting more money all the while thinking that I'm at an all-time-low in terms of providing value day-to-day? It's almost as if I deserved this salary more when I was 15 years younger and worked way harder, and that my current "senior" self deserves my starting salary 15 years ago.