Welcome to the forum and good luck with your plans

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I was told that I might be able to work on a Working Holiday Visa. I have a bachelors in Interior Design and I am seeking design jobs and/or anyone hiring. Does anyone know about this?
The Working Holiday Visa no longer exists for the UK... it has now been replaced by the Tier 5 Youth Mobility Scheme visa.
However, US citizens are not eligible to apply for it - it is only open to citizens of Australia, Canada, Japan, New Zealand, Monaco, Taiwan and Republic of Korea.
Unfortunately, this means that you may find it difficult to qualify for a visa to move to the UK.
Your easiest option would be to marry your boyfriend and get a spousal visa to live here (or get a fiance visa and marry in the UK, then switch to a extension visa to stay).
Other options would be to study for another degree in the UK on a Tier 4 student visa (but fees are expensive) or to see if you can qualify for a Tier 2 work visa (although this can be extremely difficult unless you work in a highly specialised/skilled profession or a profession that is in demand in the UK).