You're not going to be refused. If it helps, FLR(M) visas have approximately a 95% approval rate.
In 2017, there were a total of 39,251 FLR(M) partner applications lodged and 37,303 of them were approved (95% approval rate). In the first 6 months of 2018, 21,049 applications were made and 19,924 of them were approved (95% approval rate). In regards to applicants from the US, in 2017, 7,697 applications for leave to remain were made by US applicants (in all categories - work, study and family/partner), 3,181 of which were FLR(M) family/partner applications. Of those 7,697 applications only 339 were refused (giving a 96% approval rate for US applicants).
Just take what you have for the relationship, and don't worry about the rest... after all, you can't provide something you don't have anymore.
The most important part of the relationship evidence is your correspondence showing you've been living together. Anything else is an added extra/bonus to strengthen the correspondence evidence and show you have been in a relationship for longer than you have been living together.