Is it normal to lose interest in sex ?

Don't worry bro. She's gonna be fine. The only D women want is the D from Dollar.

I understand you, not nice at all.
Can happen in any age, for a week, for a month and unfortunately once in a wile for longer than that. Many reasons for that. Emotional problems of some kind, in grief for some reason, the loss of the job or money problems for instance. Nothing to do with testosterone, that's a myth.
I'm 37 and it happened to me more than once since I remember myself. As an adult might happen often and for a little longer. More than a month or so.
There are professionals helping that with with no pills or what so ever. Nutritional supplements, magic pills one can get in the net(quite dangerous),etc...etc...etc...
If you are not a prejudiced/limited person you can have a so called Swedish massage, this means a prostate massage, regulary done by men. Quite difficult to find a women doing it unless is something connected to prostitution. At least were I come from.
It worked with me a couple of times pretty well and my sex life just went on beautifully. This was recommended by a friend of mine who saw is marriage in risk coz of a similar problem. I've already recommended it to other guys and they were happy about.
I learned some of this massage centers are turned to gay people and they are nothing but gay massages. This can be avoided asking directly when you call the massage center. Easy!
This is one way to solve it without pills of some kind.
In your shoes I wouldn't panic. Relax about it, wait till it pops up again by itself, don't get anxious coz its worse.
One thing its very important. The women can help a lot trying to get out of the problem but we, men, can also keep giving them a lot of pleasure even during that time.
Here we pay for 3 sessions of 40m, 120 euros. Its cheap.

Some questions, you still masturbate? Your rod hard when you do? Do you watch porn?

WTF! At 46, you are seriously showing signs of low testoserone. See your urologist to be tested. You should have been having tests done during your annual physical. Or are you like some of the non thinkers? Don't fall for the 'T' enhancement bull. Get on a injection program right away. You will feel better, stronger, and start wanting the most natural thing in life, SEX!
Every human male is at his peak at around 22. Your 'T' starts to diminish from there. Look it up! Also, if you don't use it, you do lose it.

That shit happens to me when I get bored with a girl or if I'm too drunk but I think my problem is that I've had so many partners that it's hard to find something new and due to this I think it is very possible I may never settle down which can be sad sometimes.

I think u should see a doctor, I've seen ppl having this problem before and that's what they all did.

Male sexual dysfunction is pretty common. There are a number of possible causes, both physical and psychological. Your best first step is to mention it to your regular doc and ask for a full physical and blood work, including a testosterone test. That should narrow down the possible causes.

Viagra? Try it!

Do you still masturbate? Does your willy stay hard? Do you watch porn?