Upvote:1
Q1 Your boyfriend’s invitation: you don’t have to explain that you didn’t have a UK boyfriend last time you applied (assuming you didn’t have one) but you do have to demonstrate that there is a genuine personal relationship eg how/when you met, evidence of ongoing communication, visits by him to see you
Q2 You’ll have to provide evidence of where the money came from and that it was legally obtained, typically this is a bank statement from the person who gave you the money and possibly their pay slips or other evidence of the source of the money
Q3 Yes, you do.
Source: See Immigration Rules App V https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules