My current employer has always been good to me and me loyal to them so i feel SO guilty for even considering leaving - I know they will hate me for it and I don't want to let them down in any way
Without wanting to come across as too brash, I think you need a good reality check here.
Loyalty shouldn't come into what is essentially a business decision. If your employer was struggling for profits, or no longer had your job role available, whilst individual managers may be sad they had to let you go, the decision itself would be based on logic and their own interests - just as your decision to work there should be.
If they "hate" you for leaving, they're not professionals. These aren't your friends - you have a working relationship with them.
I am also concerned that having been there for 2 years you are slightly confusing your existing loyalty (which isn't a bad thing per se, it's just that you are of primary importance here) between different owners. You owe them nothing. You go in for an agreed benefits package, that's all - no more, no less.
Finally, having been there for 9 years, I do wonder if you are somewhat institutionalised. Perhaps because in my own industry you're considered stale for sticking with the same employer beyond 2 or 3 years (unless in a very senior position), I worry about your ability to adapt to change... you even use the phrase "better the devil" in your title. Such an attitude would set off alarm bells if I were your next employer - sorry! (I assume you managed to wow them enough at interview so that it either isn't a problem or you hid any confidence issues well - well done 
).
I wouldn't think twice about going for your new job - 18 months is a long time.
If you don't learn to adapt in your working life, you are doomed. You end up in the situation where you can't get yourself out of a hole if you find yourself in one (employer starts treating you badly, you start working with an impossible colleague, whatever). That is something that should be avoided - flexibility is the key to jobs these days, long gone are our parents' generation of jobs where it was seen as disloyal to jump ship. My parents got rewarded for long service - I have never been in a job where it has been. When employers started to remove the benefits of having long service a couple of decades ago, so should any staff member's sence of overinflated loyalty. Unfortunately, people still have that kind of attitude hanging over from that time. Perhaps it's justified if you work in e.g. the public sector (where pay increased can be linked to number of years in service), but certainly not private sector.
Employers will use this misplaced sense of loyalty ruthlessly if you let them get away with it.