If you've been 'together' for 2 years you will have plenty of proof of a relationship, this helps visa applications immenseley.
However, your first course of action is to get a Legal Seperation, otherwise I'd say it is about a 99% chane you'll be refused any visa, as all paperwork must be in order. The problem you would have with a Visitors Visa is that the interviewer will consider it a way to get out of your marriage.
I know legal sepeartions can be a problem in the Philippines, but they can be done, no need to have your ex shot!!! :blink:
Even if your single it is difficult to get a visitors visa for a Filipino.
If your serious with this boyfriend you need to either let him continue to visit you, or if you wish to come to the UK;
a) Get a legal seperation
B) Then compile as much proof of your relationship as possible. Airtickets, emails, letters, mobile txt bills, phone bills, etc,
c) Make sure b/f has proof he can support you.
d) Apply for a fiancee visa (the UK do check previous marriages in the Philippines)
e) Come here and marry
That is the only way of doing it. Do it by the book (all details listed elsewhere on the forum by Pete), and you'll be here in a few months.
As for you medical condition, the health service in this country is 100% free for anyone, from anywhere, and you'll get excellent treatment (mainly cos the nurses are Filipino ), so that is no worry.
Maybe someone else will offer more advice, but I'd say go with the above. If your serious, do it all legally and get married, so piddling about.