Not feeling the same

Me and my boyfriend have been dating almost 3 years, of which the last year and a half have been long distance. He lives in South Africa and I live in England so we’re 11 hours away on a plane, this means I’ve seen him approx. 2 months in 1 and a half years. The last two holidays we had together I was excited to see him but this time I feel a bit distant, I’m not sure if I’m falling out of love with him and I’m quite scared. We’ve been friends for 8 years and I don’t want to lose him as a friend but I’m not sure I’m as sexually attracted to him as I was before. Any advice or similar situations would be appreciated, I’m not sure what to do or how to feel.