Hi there, welcome to the forum
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Looks like you essentially know your options already. If marriage is currently out of the question, then unfortunately, there's not much else available to you.
Your options:
- study in the UK on a Tier 4 student visa yourself, though it's an expensive option (you'd need about $30,000 available to you just for the first year), and depending on your current academic qualifications, you may not meet the prerequisites because of the differences in the academic systems. For example, to get accepted into an undergraduate program, you usually need either: a US associates degree, or AP classes (level 5 or higher) in the subject(s) you wish to major in, or you have already taken college prep/college freshman/sophomore classes in the US. When I studied abroad in the US as an undergrad, I went straight from finishing 2nd year undergrad classes in the UK to taking senior and graduate classes (400- and 500-level classes) in the US.
See:
https://www.gov.uk/tier-4-general-visa/overview- Tier 2 sponsored work visa... though these can be extremely difficult to qualify for unless you work in a very highly skilled or in demand profession... just as high school math/physics teacher, doctor, nurse, academic researcher, skilled chef, professsional dancer, corporate executive etc. See:
https://www.gov.uk/tier-2-general/overview- visits to see him on a tourist visa when you can, though you'd need to be able to show you have a life, home and job to return to and aren't trying to use the visitor visa to 'live' in the UK with him. See:
https://www.gov.uk/standard-visitor-visa/overview